1. Field of the Invention
The present invention relates to an endoscopic apparatus capable of three-dimensional instrumentation for a subject region in an object of inspection.
2. Description of the Related Art
Conventionally, there are various apparatuses which use an endoscope to measure flaws on turbine blades of jet engines and the like.
In an apparatus described in U.S. Pat. No. 4,820,043, for example, an object is measured by means of a graduated transparent screen in an optical system for observation. In an apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 62-161337, on the other hand, the distance from an object is calculated on the basis of the time interval which elapses from the instant that light is projected from the distal end of an endoscope until it is reflected and returned by the object, and three-dimensional instrumentation for the object is carried out in accordance with the calculated distance.
In an apparatus described in U.S. Pat. No. 4,980,763, the size of an object is measured from the position of a shadow in a picture, the shadow being projected on the object of instrumentation. In an apparatus described in U.S. Pat. No. 4,958,932, moreover, means for changing the direction of emission of a convergent illumination light is provided such that the distance between two points on a subject can be measured by aligning a beam spot formed on an object of observation by the illumination light with a mark in the view range.
Described in U.S. Pat. Nos. 4,737,624 and 4,191,468, furthermore, are an optoelectric distance measuring apparatus with an optical measuring probe with shared optics and a range finding fiberscope for measuring the distance of a point in space from a reference plane, respectively. U.S. Pat. Nos. 4,078,864; 4,271,829, etc. are associated with this technique.
However, the prior art apparatuses described above are subject to the following drawbacks.
The apparatus described in U.S. Pat. No. 4,820,043, in which the graduated transparent screen is provided in the optical system for observation, has a drawback that images of the screen cannot be recorded. Since this apparatus cannot record necessary information for instrumentation in advance, moreover, it cannot invoke a recorded image to effect instrumentation for reconfirmation.
The apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 62-161337, cannot detect a short time required for the reciprocation of light if the measured distance is short.
According to the apparatus described in U.S. Pat. No. 4,980,763, a special mechanism must be used to project the shadow on the object of instrumentation, and the length of a reference line as a reference for measurement cannot be changed, so that a measurable distance from the distal end of the endoscope is restricted within a certain range. Thus, if the reference line length is limited, a satisfactory accuracy of measurement can be enjoyed only in an area near the distal end of the endoscope. The apparatus described in U.S. Pat. No. 4,958,932 has the same problem, due to the invariability of the reference line length. Also in an apparatus described in U.S. Pat. No. 4,271,829, its endoscope must be provided with a special mechanism for emitting light beams, and the length of a reference line as a reference for measurement cannot be changed.
According to the apparatus described in U.S. Pat. No. 4,737,624, an instrumentation error is caused by the angle between the object surface and a measuring device, so that instrumentation is limited to those objects which never change their subject surface angles. In the apparatus described in U.S. Pat. No. 4,191,468, the distal end portion of the endoscope must be provided with mirrors, so that an instrumentation head cannot be finished finely. Since the apparatus described in U.S. Pat. No. 4,078,864 is not provided with any means for reproducing instrumentation, it cannot reconfirm instrumentation.
The following is a description of major drawbacks of the aforementioned conventional apparatuses.
(1) Since a special mechanism must be attached to the distal end of the endoscopic apparatus, the apparatus requires use of a special endoscope.
(2) The distal end of the endoscopic apparatus cannot be thinned.
(3) Since the reference line length as a reference for measurement is fixed or cannot be freely changed, a satisfactory accuracy sometimes cannot be enjoyed if the distance from the distal end of the endoscope to the object to be measured varies substantially.
(4) Images and necessary data for instrumentation cannot be recorded for the reconfirmation of instrumentation results.